Machining, Measurement, and Control Laboratory

Feed drives of NC machine tools influenced by base vibration (1st report)
-- Modelling and servo analysis of feed drives with base dynamics --

Atsushi Matsubara, Masashi Umemoto, Minoru Hamamura, Jun Fujita, Yoshiaki Kai, Yoshiaki Kakino

Owing to high gain feedback control and feedforward control technology, servo response of the feed drives in NC machine tools is getting faster than that of conventional drives. However, when a large table including column or gantry is positioned by high response servo control, structural vibrations in low frequency domain are inspired and deteriorate the motion accuracy. Especially overshoot and vibration with low damping tend to appear in motion trajectory at acceleration and deceleration points. Such vibrations are likely to be generated by the dynamic combination of the machine structure as a rigid body and the floor foundation as a elastic spring and a damping. In this paper, a feed drive under the influence of base dynamics is investigated in a existing horizontal machining center by using FEM and experimental modal analysis. By creating a servo simulation model with the drive and base, vibrations at positioning are estimated and have a good agreement with measured ones. By analyzing the servo model it is found that the vibration is due to the coupling of base dynamics and feed dynamics.